Beacon providing visual direction information

ABSTRACT

An anti-collision beacon for aircraft or other applications. A pair of coaxially displaced filters are sequentially illuminated to provide flashes of light which uniquely identify the quadrants of the filter relative to the position of an observer. The time at which a particular color flash occurs, in relation to the preceding and succeeding contrasting color flashes, varies proportionately to the viewing angle within each quadrant. Another embodiment of this filter provides visual aircraft landing glide-slope information.

United States Patent Turner, Jr.

[451 Dec.'19, 1972 [54] BEACON PROVIDING VISUAL DIRECTION INFORMATIONCharles J. Turner, In, Atlanta, Ga.

Lockheed Aircraft Corporation, Burbank, Calif.

Filed: Nov. 20, 1970 Appl. No.: 91,260

Inventor:

Assignee:

[52] US. Cl. ..340/25, 340/366 F, 240/l.2,

240/7.7 Int. Cl. ..G08g 5/00 Field of Search ..340/25, 26, 27, 366 F;

[56] References Cited UNITED STATES PATENTS 3,436,729 4/1969 Zurcher..340/25 2,365,038 12/1944 Adler,Jr. ..340/25 2,096,755 10/1937Parsberg.... ...340/25 3,012,224 12/1961 Ferguson ..240/l.2

Primary Examiner-John W. Caldwell Assistant Examiner-Robert J. MooneyAttorney-Roger T. Frost and George C. Sullivan [57] ABSTRACT Ananti-collision beacon for aircraft or other applications. A pair ofcoaxially displaced filters are sequentially illuminated to provideflashes of light which uniquely identify the quadrants of the filterrelative to the position of an observer. The time at which a particularcolor flash occurs, in relation to the preceding and succeedingcontrasting color flashes, varies proportionately to the viewing anglewithin each quadrant. Another embodiment of this filter provides visualaircraft landing glide-slope information.

14 Claims, 4 Drawing Figures WHITE I6 PATENTEU 0E: 19 m2 SHE U 1 0F 2 DE! E U U DDUDEIQDEIUEIEIEIUUUUEIUUUEIEI WHITE an-bl: 1

WHITE glint RE D INVENTOR. CHARLES J. TURNER,JR

BY H n 1 will Attorney m B R w R E m E W Sim; "m T E B E l R M 3 R E x;LT M H A E P. E A W o 5 B 0 NM 0 D I M I! L .0. D 9 E G A 4 S in: D 1 RE R E E R w R I N D m 5 F E U a E R G a G m w w m E R W E v H B 5 W M E-muw 0% 8H IOWB A PATENTEDHEC 19 1912 sum 2 o 2 GREEN) AMBER- 4 E w E mO I F (GREEN) 270 (GREEN-AMBER) INVESTOR. CHARLES J. TURNER,JR

BEACON PROVIDING VISUAL DIRECTION INFORMATION This invention relates ingeneral to visual beacons and in particular to an anti-collision beaconof the type mounted on vehicles such as aircraft or the like.

The problem of avoiding a mid-air collision between two aircraft isgrowing apace with the increased traffic in flights by general,commercial, and military aircraft. It is important for the aircraftpilot that he be able to see other aircraft in his vicinity so that hecan determine whether the attitude and course of these aircraft requirethat he take evasive action to avoid an in-flight collision. Therotating red beacon now used on aircraft provides a bright red flashinglight to alert the pilot to the presence of the aircraft, but thesebeacons are omnidirectional, i.e., a person observing the beacon cannotdetermine the heading of the other aircraft merely by observing thebeacon flash. Accordingly, the pilot must observe the displacement ofeach beacon flash relative to the preceding beacon flashes to determinewhich way the aircraft is moving before he can decide whether he shouldtake evasive action, and the difficulty of such observation iscompounded by the relative velocities of the two aircraft.

Various electronic collision avoidance systems have been proposed which,if used, would provide the pilot with an instrument panel indication ofa potential collision situation or of the proper action to be taken toavoid another aircraft. To be effective, however, systems of this kindrequire that all aircraft flying in a given area must be equipped withelaborate and expensive timing and transponder equipment which is beyondthe financial means of most general aviation operators. In thealternative, at least one prior art visual beacon has been proposedwhich flashes a different color for each quadrant but which provides noinformation about the aircraft orientation within a particular quadrantand which, therefore, cannot inform an observer of changes in theattitude of the aircraft until the position of the aircraft has moved toa different quadrant, as viewed by the observer.

Accordingly, an object of the present invention'is to provide animproved visual beacon.

It is another object of this invention to provide a visual beacon whichpresents a precise and unambiguous indication of angular positionrelative to an observer of the beacon.

Still another object of this invention is to provide a visual beacon forinstallation on an aircraft to produce flashes of illumination providingan observer of such aircraft with an unambiguous indication of theheading of the aircraft.

Yet another object of the present invention is to provide an improvedoptical aircraft landing approach guidance apparatus.

Still another object of this invention is to provide an opticalglideslope apparatus which provides a pilot with an optical indicationof the direction and the extent of any deviation from a desiredglideslope.

Other objects and many of the attendant advantages of the presentinvention will become apparent from examining the following descriptionand drawings in which:

FIG. 1 shows a portion of an aircraft fuselage equipped with beaconsaccording to an embodiment of the present invention;

FIG. 2 shows an exploded isometric schematic view of one of the beaconsof FIG. 1',

FIG. 3 shows a modified plan view of the FIG. 2 beacon'with one of theannular filter members depicted as being reduced in diameter to aid in'illustrating the construction and operation of the beacon; and

FIG. 4 shows an elevation view of another embodiment of the presentinvention as used to define an optical glideslope for aircraft landingpurposes.

Stated generally, the beacon of the present invention comprises a pairof color filters which are axially displaced from each other. A separaterotating or otherwise movable illumination source is provided withineach of the filters, and the filters are divided into segments ofdistinctive colors which are oriented with respect to each other so thatthe color and timing of the flashes produced by the filters of thebeacon are uniquely dependent upon the azimuthal position of an observerrelative to the beacon.

Turning now to FIG. 2, a specific embodiment of a beacon according tothe present invention is shown in exploded view generally at 10, itbeing understood by those skilled in the art that each such beacon inactual construction would be packaged in a streamlined envelope suitablefor mounting, as shown at 1 l and 12 on the exterior of an aircraft 13shown in FIG. 1. Each beacon 10 includes a lower segmented filter 15 andan upper segmented filter 16, with the upper segmented filter 16 beingpositioned above and coaxial with the lower segmented filter 15. Each ofthe segmented filters in the depicted embodiment preferably is shapedlike an annular ring to appear somewhat like a hoop, and the filters 15and 16 preferably are of equal diameter, although the filter 16 isdeliberately depicted in FIG. 3 as being smaller in diameter than thefilter 15 to aid in describing the color arrangement of the two filters.

Each of the segmented filters 15 and 16 is divided into four filtersegments 15a, 15r, 15w, 15g and 16a, 16r, 16w, and 16g, respectivelycorresponding to the selected filter segment colors amber, red, white,and green. These particular colors were chosen because aircraft pilotsare accustomed to the convention of a green light representing the rightside of the aircraft and a red light representing the left side of theaircraft, although other colors could be selected as desired. Althougheach of the filter segments occupies or one quadrant of the respectivesegmented filter, it is apparent in FIG. 3 that the juncture betweenadjacent filter segments does not coincide with the depicted azimuthlines, with 0 representing the nose of the aircraft and representing thetail of the aircraft on which the beacon is to be mounted. For example,the amber filter segment 15a adjoins the red filter segment 15r at apoint approximately 8 removed from the O or heading direction, while thegreen segment 16g of the upper filter adjoins the amber segment 16a atan azimuth location of about 252, or 8 in the negative direction fromthe 0 line. The purpose and the function of this filter segment angularoffset is explained below.

A lower lamp platform 20 is mounted for rotation within the lowersegmented filter 15. The lower lamp platform 20 carries a pair ofelectric lamps 21 and 22 mounted 180 apart on the platform, with each ofthe lamps having corresponding reflectors 23 and 24. An

upper lamp platform 25 is mounted for rotation within the uppersegmented filter 16, with the upper lamp platform 25 containing a pairof diametrically opposed lamps 26 and 27, along with correspondingreflectors 28 and 29. The lamp platforms 20 and 25 are driven forrotation in opposite directions by any suitable mechanism, such as anouter shaft 30 connected to drive the lower lamp platform and aconcentric inner shaft 31 connected to drive the upper lamp platform.The drive shafts 30 and 31 are respectively connected to gears 32 and 33counter-rotatably driven by the drive gear 34 and the motor 35.Electricity is supplied to the lamps on each of the lamp platformsthrough suitable mechanisms of the type known to those skilled in theart, such as slip rings or the like. The lamps and reflectors arealigned so that the path through which the beams of illumination fromthe lamps 21 and 22 move is substantially spatially coextensive with thepath through which the beams from the lamps 26 and 27 move.

The operation of the beacon embodiment depicted in FIGS. 2 and 3 is nowdescribed. If the lamp platforms 2 and 25 are initially aligned so thatthe lamps 21, 22 and 26, 27 are initially aligned along the fore-aftaxis'of the aircraft on which the beacon is installed, then the lampswill also be aligned at each 90 of displacement from the initialposition upon counter-rotation of the lamp platforms. FIG. 2, forexample, shows the relative positions of the lamps when the lampplatforms have been rotated 90 from the position shown in FIG. 3. Anobserver positioned at 0 azimuth with respect to the aircraft, i.e.,dead ahead of the aircraft, sees two concurrent amber flashes producedbythe light from the lamp 22 passingthrough the lower amber filtersegment 15a and the light from the lamp 26 passing through the upperamber filter segment 16a as these lamps simultaneously sweep past theoverlapped portions of the respective amber filter segments. This sameobserver will see another set of concurrent amber flashes when each ofthe lamp platforms has rotated 180 to sweep the lamps 21 and 27,respectively, simultaneously across the amber filter segments 15a and16a. The observer thus knows by observing the concurrent amber flashesfrom the beacon that the aircraft is on a collision heading with himunless there is enough altitude separation to permit the aircraft topass safely above or below him.

Assume next that the observer is at of azimuth displaced from theheading of the aircraft. The lamp 26 crosses the l5 line in a clockwisedirection just slightly before the lamp 22, moving in the oppositedirection, crosses the 15 line. Accordingly, the observer stationed onthe 15 line sees an amber flash from the upper filter segment 16a justslightly before seeing a red flash from the lower filter segment l5r,and the amber-just-before-red flash sequence advises the observer thathe is just to the left of the aircrafts heading.

If the observer now moves to the 30 azimuth line, for example, it can beseen that the period between the time that the lamp 26 crosses the 30line and the time that the lamp 22 crosses the same line is greater thanthe corresponding period for the 15 line. Therefore, the period of timebetween the amber and the red flashes also increases, informing theobserver of his present azimuth position relative to the aircraft. Whenthe observer reaches the 45 line, as shown in FIG. 3, the elapsed timebetween the passage of any of the lamps across the 45 line and thepassage of the next lamp across that line is equal, and so an observerat the 45 line sees consecutive amber and red flashes with an equal timeperiod between each such flash.

If the observer next moves to the line, where he is positioned off theleft wing of the aircraft, he will see concurrent red flashes as thelamps 22 and 27 (or 21 and 26) cross the 90 line at the same time toilluminate the overlapped portions of the red filter segments l5r andl6r. In a similar manner, an observer stationed at 180 azimuth, or deadastern of the aircraft, sees concurrent white flashes; and an observerstationed at 270 azimuth, or off the right wing of the aircraft, seesconcurrent green flashes. Observation positions at intermediatelocations in the quadrants will produce variably timed sequences of thecolors observed at the four.90 locations, such color sequences beingnoted parenthetically in FIG. 3. It is apparent that a unique andunambiguous sequence of color flashes is produced for any azimuthposition of the beacon embodied in FIGS. 2 and 3, and an observer whohas learned the meaning of the various color flash sequences is immediately aware of his position relative to an aircraftmounted beaconproducing, for example, a. greenamber flash sequence.

Another embodiment of the present invention, as shown in FIG. 4, can beused to provide a visual glideslope beacon to aid a pilot in attainingthe proper glide angle for landing his aircraft. The beacon embodimentschematically shown in elevation view generally at 40 includes a firstsegmented filter 41 and a second segmented filter 42. The segmentedfilters 41 and 42 are coaxially displaced from each other and preferablyare of equal diameter comparable to the segmented filters l5 and 16 ofthe prior embodiment, although the second segmented filter 42 is drawnin FIG. 4 with reduced diameter to facilitate understanding of theoperation of the depicted embodiment. A first rotating lamp platform 43is positioned within the segmented filter 41 and carries three lamps 44,45, and 46, along with suitable reflectors (not shown), positioned atintervals apart. A second lamp platform 47 is posi tioned for rotationwithin the second segmented filter 42 with three lamps 48, 49, and 50,also provided with suitable reflectors, positioned at intervals 120apart on the second lamp platform. All of the first segmented filter 41is opaque except for a green filter segment 41g and an amber filtersegment 41a, and all of the second segmented filter 42 is opaque exceptfor an amber filter segment 42a and a red filter segment 42r. Sinceamber is the color selected in this embodiment to inform the pilot thathe is flying the proper glide path, the two amber filter segments 41aand 420 are dimensioned to overlap the glideslope centerline 51 asshown. Each of the lamp platforms 43 and 47 is rotated in oppositedirections by a suitable mechanism such as shown in FIG. 2, andelectricity is supplied to the lamps on the rotating lamp platforms by asuitable mechanism.

Assuming that a pilot is flying his aircraft along the glideslopecenterline 51, he sees only concurrent amber flashes because each lampon the first lamp platform 43 crosses the centerline 51 at the same timethat a corresponding lamp on the second lamp platform 47 crosses thatcenterline. If the pilot drops below the desired glideslope centerline51 to be flying along a line such as 52, the lamp 50 crosses the line 52and produces a red flash through the filter segment 42r just before thelamp 46 crosses the line 52 to produce an amber flash through the filtersegment 41a. The pilot thus is advised by the red-immediatelyfollowed-byamber flash sequence that he has dropped just below the lowerlimit of the desired glideslope range. In a similar manner, if the pilotis flying along a line of flight which passes through the green filtersegment 41g, he will perceive a green-amber flash sequence which adviseshim that he is flying above the desired glide path. As the extent ofdeparture from the desired glideslope increases in either direction, thegreen-amber or red amber timing ratio changes so that the pilot is alsoadvised of the extent of the flight path departure.

It will be apparent that the glideslope beacon of FIG. 4 can be modifiedto provide localizer information simply by rotating the beacon 90 aroundthe centerline 51. It also follows that a pair of the FIG. 4 beacons canbe used together to provide both glideslope and localizer information,in which case distinctive and separate colors should be used in the twobeacons.

The use of three lamps on each of the platforms in the FIG. 4 embodimentprovides a greater change in flash rate for a given angular displacementfrom the glideslope centerline than would be provided through the use oftwo lamps per platform. A deviation of plus or minus 30 from thecenterline 51 thus produces an equal-duration green-amber or red-ambercolor flash,

respectively, whereas a deviation of 45 is required to produce a flashsequence of equal duration when each platform contains only two lamps.The embodiment of FIG. 4 could be provided with fewer or more lamps perplatform, depending upon the desired amount of change in the flash ratefor a given amount of displacement from the centerline.

Other physical construction configurations can be used to produce theresults described herein. For example, the hoop-shaped filters could bereplaced by discshaped filters aligned with appropriate light sources.If such disc-shaped filters were not perpendicular to the plane throughwhich the beacon flashes must sweep, prisms or other suitable opticaldevices could be used to change the direction of the light beams passingthrough the filters.

The amount of overlap or offset between filter seg ments of the samecolor, shown herein as 16", can be varied to produce the desired visualflash. The beam width of the lamp-reflector combination, as well as theangular velocity of the lamp platforms, are factors to be considered inselecting the amount of filter segment overlap.

If it is necessary to use two beacons on an aircraft, as shown in FIG.1, the rotations of the two beacons should be synchronized so that anobserver positioned to view both beacons will see the same flashsequence from each beacon at the same time.

Although the present invention is depicted herein with counter-rotatinglamp platforms, similar results are obtainable by using platformsrotating in the same direction. In this case, the number of lamps oneach of the two platforms is unequal and the ratio of angular velocityof the two platforms is inversely proportional to the ratio of thenumber of lamps on the platforms.

It should be understood, of course, that the foregoing relates only topreferred embodiments of the invention and that numerous modificationsor alterations may be made therein without departing from the spirit andthe scope of the invention, as set forth in the appended claims.

What is claimed is: 1. An optical beacon for selectively casting flashesof illumination along a field of view, said beacon comprising:

a first illumination means operative to produce a first beam ofillumination which periodically traverses a first predetermined pathalong the field of view;

first color filter means associated with the beacon and traversed by thebeam of illumination from said first illumination means to impart colorinformation to said first beam;

a second illumination means operative to produce a second beam ofillumination which periodically traverses a second predetermined pathalong the field of view;

second color filter means associated with the beacon and traversed bythe beam of illumination from said second illumination means to impartcolor information to said second beam;

said first and second illumination means being positioned relative toeach other to cause thefirst predetermined path traversed by the firstbeam of illumination to be substantially coextensive with the secondpredetermined path traversed by the second beam of illumination; and

each of said first and second color filter means being operative toimpart color information to its respective traversing beam ofillumination so that at least some of the locations along saidcoextensive first and second predetermined path are periodicallyillaminated by a unique time sequence of color flashes from said beamsof illumination.

2. An optical beacon for selectively casting flashes of illuminationalong a field of view, said beacon comprismg:

a first support means disposed for rotation on an axis;

at least one illumination means positioned on said first support meansto direct a first beam of illumination along a first rotative path inthe field of view;

first filter means positioned to be traversed by said first beam ofillumination as said first support means is rotated;

said first filter means being divided along the direction of beammovement into a plurality of color filter segments so that the color ofthe first beam of illumination in the field of view is determined by thecolor of the filter segment through which the first beam passes;

a second support means disposed for rotation on said axis;

at least one illumination means positioned on said second support meansto direct a second beam of illumination along a second rotative path inthe field of view;

each of said illumination means being disposed so that said first andsecond rotative paths of beam movement are substantially spatiallycoextensive with each other;

second filter means positioned to be traversed by said second beam ofillumination as said second support means is rotated;

said second filter means being divided along the direction of beammovement into a plurality of color filter segments so that the color ofthe second beam of illumination is determined by the color of the filtersegment through which the second beam passes; and

motive means operatively associated with said first and second platformsto impart rotation to both of said platforms to cause the period of timebetween the arrival of said first beam at a point in the field of viewand the arrival of said second beam at the same point in the field ofview to be constant for such point and to be a function of the locationof such point in the field of view.

3. Apparatus as in claim 2, wherein said motive means is operative tocause said first and second support means to counter-rotate at equalrotational speed.

4. Apparatus as in claim 3, wherein each of said support means mounts aplurality of said illumination means positioned to direct acorresponding number of beams of illumination spaced equidistant aroundsaid axis of rotation.

5. Apparatus as in claim 2, wherein each of said illumination means isoperative to direct a plurality of beams of illumination substantiallyradially of said axis and spaced angularly equidistant around said axisof rotation.

6. Apparatus as in claim 5, wherein said motive means is operative tocause each of said support means to counter-rotate at equal rotationalspeed, and wherein the number of beams of illumination directed by saidfirst illumination means is equal to the number of beams of illuminationdirected by said second illumination means.

7. Apparatus as in claim 5, wherein said second illumination meansdirects a number of beams of illumination which is unequal to the numberof beams of illumination directed by said first illumination means, andsaid motive means is operative to cause each of said support means torotate in the same direction such that the ratio of the angular velocityof the first support means relative to the angular velocity of thesecond support means is inversely proportional to the ratio of thenumber of beams of illumination directed by the first illumination meansrelative to the number of beams of illumination directed by the secondillumination means.

8. Apparatus as in claim 2, wherein:

said first filter means is angularly aligned on said axis with respectto said second filter means so that the division between at least onepair of contiguous filter segments of said first filter means isangularly aligned with a filter segment of said second filter means.

9. Apparatus as in claim 8, wherein one of said contiguous filtersegments is the same color as said angularly aligned filter segment ofsaid second filter means.

10. Apparatus as in claim 2, wherein:

said filter segments of said first filter means are disposed to providea first angular sequence of certain colors to be traversed by said firstbeam of illumination; said filter segments of said second filter meansare disposed to provide a second angular sequence of certain colorsidentical to said first angular sequence. of colors and to be traversedby said second beam of illumination; and

said second sequence of certain colors being angularly displaced on saidaxis a predetermined amount with respect to said first sequence ofcertain colors.

11. Apparatus as in claim 10, wherein said field of view substantiallycomprises a circle around said axis, and where the respective filtersegments of each of said first and second filter means is disposed toprovide a circular sequence of said certain colors.

12. Apparatus as in claim 11, wherein the angular extent of all of saidfilter segments is the same.

13. Apparatus as in claim 12, wherein each of said filter segments isapproximately ninety degrees in angular extent, so that each of saidfilter means includes four filter segments to provide an angularsequence of four colors.

14. Apparatus as in claim 13, wherein:

said motive means is operative to cause each of said support means tocounter-rotate at equal rotational speed; and

each of said illumination means is operative to direct a pair ofdiametrically opposed beams of illumination through the respectivefilter means.

l l I II!

1. An optical beacon for selectively casting flashes of illuminationalong a field of view, said beacon comprising: a first illuminationmeans operative to produce a first beam of illumination whichperiodically traverses a first predetermined path along the field ofview; first color filter means associated with the beacon and traversedby the beam of illumination from said first illumination means to impartcolor information to said first beam; a second illumination meansoperative to produce a second beam of illumination which periodicallytraverses a second predetermined path along the field of view; secondcolor filter means associated with the beacon and traversed by the beamof illumination from said second illumination means to impart colorinformation to said second beam; said first and second illuminationmeans being positioned relative to each other to cause the firstpredetermined path traversed by the first beam of illumination to besubstantially coextensive with the second predetermined path travErsedby the second beam of illumination; and each of said first and secondcolor filter means being operative to impart color information to itsrespective traversing beam of illumination so that at least some of thelocations along said coextensive first and second predetermined path areperiodically illuminated by a unique time sequence of color flashes fromsaid beams of illumination.
 2. An optical beacon for selectively castingflashes of illumination along a field of view, said beacon comprising: afirst support means disposed for rotation on an axis; at least oneillumination means positioned on said first support means to direct afirst beam of illumination along a first rotative path in the field ofview; first filter means positioned to be traversed by said first beamof illumination as said first support means is rotated; said firstfilter means being divided along the direction of beam movement into aplurality of color filter segments so that the color of the first beamof illumination in the field of view is determined by the color of thefilter segment through which the first beam passes; a second supportmeans disposed for rotation on said axis; at least one illuminationmeans positioned on said second support means to direct a second beam ofillumination along a second rotative path in the field of view; each ofsaid illumination means being disposed so that said first and secondrotative paths of beam movement are substantially spatially coextensivewith each other; second filter means positioned to be traversed by saidsecond beam of illumination as said second support means is rotated;said second filter means being divided along the direction of beammovement into a plurality of color filter segments so that the color ofthe second beam of illumination is determined by the color of the filtersegment through which the second beam passes; and motive meansoperatively associated with said first and second platforms to impartrotation to both of said platforms to cause the period of time betweenthe arrival of said first beam at a point in the field of view and thearrival of said second beam at the same point in the field of view to beconstant for such point and to be a function of the location of suchpoint in the field of view.
 3. Apparatus as in claim 2, wherein saidmotive means is operative to cause said first and second support meansto counter-rotate at equal rotational speed.
 4. Apparatus as in claim 3,wherein each of said support means mounts a plurality of saidillumination means positioned to direct a corresponding number of beamsof illumination spaced equidistant around said axis of rotation. 5.Apparatus as in claim 2, wherein each of said illumination means isoperative to direct a plurality of beams of illumination substantiallyradially of said axis and spaced angularly equidistant around said axisof rotation.
 6. Apparatus as in claim 5, wherein said motive means isoperative to cause each of said support means to counter-rotate at equalrotational speed, and wherein the number of beams of illuminationdirected by said first illumination means is equal to the number ofbeams of illumination directed by said second illumination means. 7.Apparatus as in claim 5, wherein said second illumination means directsa number of beams of illumination which is unequal to the number ofbeams of illumination directed by said first illumination means, andsaid motive means is operative to cause each of said support means torotate in the same direction such that the ratio of the angular velocityof the first support means relative to the angular velocity of thesecond support means is inversely proportional to the ratio of thenumber of beams of illumination directed by the first illumination meansrelative to the number of beams of illumination directed by the secondillumination means.
 8. Apparatus as in claim 2, wherein: said firstfilter means is angularly aliGned on said axis with respect to saidsecond filter means so that the division between at least one pair ofcontiguous filter segments of said first filter means is angularlyaligned with a filter segment of said second filter means.
 9. Apparatusas in claim 8, wherein one of said contiguous filter segments is thesame color as said angularly aligned filter segment of said secondfilter means.
 10. Apparatus as in claim 2, wherein: said filter segmentsof said first filter means are disposed to provide a first angularsequence of certain colors to be traversed by said first beam ofillumination; said filter segments of said second filter means aredisposed to provide a second angular sequence of certain colorsidentical to said first angular sequence of colors and to be traversedby said second beam of illumination; and said second sequence of certaincolors being angularly displaced on said axis a predetermined amountwith respect to said first sequence of certain colors.
 11. Apparatus asin claim 10, wherein said field of view substantially comprises a circlearound said axis, and where the respective filter segments of each ofsaid first and second filter means is disposed to provide a circularsequence of said certain colors.
 12. Apparatus as in claim 11, whereinthe angular extent of all of said filter segments is the same. 13.Apparatus as in claim 12, wherein each of said filter segments isapproximately ninety degrees in angular extent, so that each of saidfilter means includes four filter segments to provide an angularsequence of four colors.
 14. Apparatus as in claim 13, wherein: saidmotive means is operative to cause each of said support means tocounter-rotate at equal rotational speed; and each of said illuminationmeans is operative to direct a pair of diametrically opposed beams ofillumination through the respective filter means.